What crossed my mind is that, Karan felt Asad's feelings for Zoya for two months before the beautiful mangalpur track happened where we got our first ZOYAAA dahad, he felt Asad's love at first sight for Zoya, he felt Asad's gradual understanding of Zoya post Akram fiasco, he got the chance to live and feel Asad from the beginning and for the amazing actor he is he emoted Asad wonderfully onscreen. But that's not the case for Raquesh, he hasn't felt Asad, he hasn't felt Asad's passion for Zoya and on the first day of shoot he got play this intense scene. I guess gradually as he understands his character better we will get to see that passion filled pukaar for Zoya.
This is purely my opinion and I don't intend to defend or offend any actor because I may not be a die-hard KSG fan but I have always maintained that he is the best actor on television right now.
Raquesh is a very good replacement and he will definitely do justice to his role, I don't expect him to be like Karan, because every actor has their own style, way of emoting and voice.
Karan will always be remembered as Asad, and Raquesh is already been accepted as Asad by me atleast.